This invention relates to a precision-stitch sewing machine, particularly useful for attaching hems to wearing apparel.
As is known, the attachment of hems to garments or articles of clothing is generally performed on linking machines, which have an annular set of needles arranged to rotate in synchronization with a linking assembly and to which a hem is fed which may be folded over a flap of a garment being sewn.
Such an operation, in view of its high cost, can only be justified where a high quality finish work is sought, and in most instances, hems are instead applied by means of sewing machines.
In the latter case, sewing machines may include a feeding assembly for feeding in a garment to be sewn which cooperates with a hem entraining assembly for an optionally folded hem, the latter assembly being located upstream of a sewing assembly, thereby an edge or flap of the garment to which the hem is to be attached is enveloped between two flaps of the folded over hem.
The entraining action is applied to the hem via claws or entraining belts, and on one flap of the folded hem, in general the lower flap thereof.
Consequently, already after a short length of the hem has been sewn, the upper flap, which is initially set to exactly match the lower flap, tends to move out of alignment with the latter owing to the friction exerted between said upper flap and pressure shoe of the sewing assembly, and owing to its entrainment solely relying on cooperation with the entrainment action exerted on the lower flap. This results in the need for frequent manual interventions to restore the two flaps to their proper positions and in the likelihood or faulty seams which lower the value of the article of clothing produced.
It may also be important to differentiate the feed rate of the garment from the entrainment rate of the hem, in order to impart the produced garment with different degrees of elasticity at areas thereof whereat stresses are more likely to occur.